"Tesofensine produces a weight loss of approximately 10 percent more than placebo and diet in obese patients," said lead researcher Dr. Arne Astrup, from the Department of Human Nutrition, Faculty of Life Sciences, at the University of Copenhagen. Other drugs produce only about 5 percent weight loss, Astrup noted.

This drug could replace the need for gastric bypass surgery in some obese patients. "There is an enormous gap between the existing weight-loss compounds and gastric surgery," Astrup said. "Tesofensine could close that gap. If you combine the drug with an effective diet, you could probably reach the 20 percent weight loss seen in gastric surgery."

"Tesofensine could compete with gastric surgery and be offered to those who are below the threshold for surgery or for patients who do not wish [to have] gastric surgery," Astrup said. "There are also patients who cannot tolerate gastric surgery."

The report was published in the Oct. 23 online issue of The Lancet.

For the study, Astrup's team conducted a phase II trial in which they randomly assigned 203 obese patients to receive three different daily doses of tesofensine or placebo. The participants were also put on a low-energy diet.

Among the 161 who completed the trial, those who received tesofensine lost more weight than those receiving placebo. Over 24 weeks, those receiving the lowest dose of tesofensine (0.25 milligrams) lost 14.7 pounds, while those taking 0.5 milligrams lost 25 pounds, and those taking the highest dose (1 milligram) lost 28 pounds. People receiving placebo lost less than 5 pounds.

The weight loss among people who took 0.5 or 1 milligram of tesofensine was double that of weight loss seen with the currently available diet drugs Acomplia (rimonabant) or Meridia (sibutramine), the researchers said.

People taking the highest dose of tesofensine experienced a rise in blood pressure. Other side effects of the drug included dry mouth, nausea, constipation, hard stools, diarrhea and insomnia.

Astrup believes that the 0.5 milligram dose is the best, because it produced weight loss with the fewest side effects.

Early evidence shows that people who stay on the drug maintain their weight loss and may even continue to lose weight, Astrup said.

Once starting the drug, people would need to keep taking it to maintain the benefit, Astrup said. "There is no treatment that is working beyond its taking. This is true for all anti-diabetic medication, hypertension medication and everything, including anti-obesity drugs," he said. "It's a long-term treatment, and, in some cases, a permanent treatment to keep body weight down."

Tesofensine works by inhibiting the neurotransmitters noradrenalin, dopamine and serotonin in the brain. In turn, this suppresses hunger, leading to an energy deficit which burns excess body fat. The drug's effect was first noticed in trials involving Alzheimer's and Parkinson's patients.

Larger clinical trials of tesofensine are expected to begin next year, Astrup said.

Astrup noted that Neurosearch, the maker of tesofensine, is seeking approval for the drug in the United States and Europe. Astrup is a paid consultant for Neurosearch and also owns stock in the company.

Dr. David L. Katz, director of the Prevention Research Center at Yale University School of Medicine, thinks that the true test of any diet or drug is its ability to keep weight off over time.

"Losing weight, in the short term, though not easy, is not all that challenging," Katz said. "Any diet that restricts choice will tend to work, from low fat, to low carb, to cabbage soup or grapefruit, and a number of drugs can provide this effect as well, including, it seems, tesofensine," he said.

But the real test is sustainable weight control over the long term, Katz said. "This six-month study cannot tell us if tesofensine will pass that test," he noted.

This trial did find that tesofensine increased heart rate and blood pressure slightly, and reduced lean body mass along with fat mass. "These effects are all of potential concern," Katz noted.

"Additional study is needed to tell us what place tesofensine might occupy among the strategies available to facilitate sustainable, healthful weight loss," Katz said. "Though promising, this study does not yet get us there."